EFFECTS OF BIOCHAR AND NPS FERTILIZER ON YIELD AND YIELD RELATED TRAITS OF POTATO (Solanum tuberosum L.) AT HARAMAYA, EASTERN ETHIOPIA

Potato is an important food and export crop in East Hararghe. However, its yield is very low due to several factors among which low soil fertility and poor fertilizer management practice applied by growers are major ones. Therefore, a field experiment was conducted to assess the effects of biochar and NPS fertilizer on yield, yield-related traits, and quality of potatoes and to estimate the cost-benefit of combined application of biochar and blended NPS fertilizer for potato production at Raare crop research field of Haramaya University, in 2022 main cropping season. Treatments consisted of four levels of biochar (0, 10, 20, and 30 t ha_1) and five levels of blended NPS (0, 50, 100, 150, and 200 kg ha_1) and laid out in a Split Plot Design replicated three times per treatment. Urea fertilizer at the rate of 100 kg ha_1 was applied to all plots except control plot. Biochar was assigned as the main plot and NPS fertilizer was assigned as sub-plots. The Potato variety named “Bubu” was used for the study. Results showed significant interaction effects of biochar and blended NPS fertilizer on most of the parameters studied. However, the main stem number, leaf area index, specific gravity, tuber dry matter, and total starch content were significantly influenced by the main factors of NPS fertilizer and biochar. An increasing rate of biochar and NPS blended fertilizer enhanced the main stems number, leaf area index, specific gravity, tuber dry matter, and total starch content. An increasing rate of biochar combined with NPS blended fertilizer increased plant height, days to 50% flowering, days to 90% of maturity, average tuber number, average tuber weight, marketable tuber yield, total tuber yield, the proportion of medium and large tuber size. On the other hand, increasing the rate of biochar combined with blended NPS fertilizer reduces the proportion of small tuber size and unmarketable tuber yield. However, for most parameters, the highest values were obtained at the highest rate of biochar and NPS blended fertilizer. The results of the partial budget analysis showed the application of 30 t ha_1 biochar in combination with 200 kg ha_1 NPS fertilizer gave the highest marketable tuber yield that could offer the highest net benefit of 531772 Birr per hectare and marginal rate of return (MRR) of 336.90% more than acceptable rate of return. Thus, it is possible to recommend the application of the combined application of 30 t ha_1 biochar in combination with 200 kg ha_1 NPS fertilizer for the production of the Bubu variety in the study area.